376 



Geological Society. 



necessary to form, they had not agreed with each other as to 

 the individual beds inclosed in one group. Thus, some had 

 formed a group (which they called the ferruginous sand) of the 

 sands above and below the weald clay ; while others had at- 

 tached the name of Ferruginous sand to those beloiv the weald 

 clay only. He had also reason to fear, that an error had been 

 committed in not identifying the beds which are called the fer- 

 ruginous sand on the west of the chalk ; as the Carstone, Wo- 

 bourn sand, and the Farringdon bed, with the beds in the 

 wealds of Kent and Sussex, to which the name of green sand 

 had been given. 



The following is the table of equivalent beds above alluded 

 to. 



Nov. 19. — A paper was read " On the Purbeck and Port- 

 land beds," by Thomas Webster, Esq., Sec. G.S. 



The author observed, that the great general features of the 

 geology of the Isle of Purbeck had been already traced out by 

 him in his letters to Sir H. Englefield. He now confined 

 himself to some details respecting the series of limestone beds 

 in the Isle of Purbeck, and to those in the Isle of Portland. 



He then proceeded to give a description of the strata from 

 which the well known Purbeck stone used in London for side 



pavements, 



